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The development of karst is a complex system driven by the dissolution of a host rock and the subsequent removal of dissolved matter by moving water. It is the process that, at various stages, initiates or triggers associated processes including erosion, collapse and subsidence. The dissolution of sulphate rocks proceeds by different mechanisms and at different rates to those associated with the dissolution of carbonate rocks. For each rock type different factors influence the process. This chapter is an attempt to summarise the present knowledge of the dissolution chemistty and kinetics of gypsum and anhydrite. These are important for the genetic interpretation of karst features in these rocks. The gypsum-anhydrite-gypsum transitions and recrystallization processes are also addressed, because of their importance to karst development.Many studies have been undertaken on the solubility and dissolution of sulphate minerals, in the context of construction engineering and karst processes. Important works include these of

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Conceptual and respective quantitative models of speleogenesis/karstifi cation developed for unconfi ned aquifers do not adequately represent speleogenesis in confi ned settings. A conceptual model for speleogenesis in confi ned settings is suggested, based on views about hydraulic continuity in artesian basins and close cross-formation communication between aquifers in multi-storey artesian systems. Soluble units sandwiched between insoluble porous/fi ssured formations (common aquifers) initially serve as low permeability beds separating aquifers in a confi ned system. Conduits evolve as result of vertical hydraulic communication between aquifers across the soluble bed ("transverse speleogenesis"). Recharge from the adjacent aquifer is dispersed and uniform, and fl ow paths across the soluble bed are rather short. There is a specifi c hydrogeologic mechanism inherent in artesian transverse speleogenesis (restricted input/output) that suppresses the positive fl ow-dissolution feedback and hence speleogenetic competition in fi ssure networks, and accounts for the development of more pervasive channelling in confi ned settings, of maze patterns where appropriate structural prerequisites exist. This is the fundamental cause for the distinctions between cave morphologies evolving in unconfi ned and confi ned aquifers and for eventual distinctions of karstic permeability, storage characteristics and fl ow system behaviour between the two types of aquifers. Passage network density (the ratio of the cave length to the area of the cave fi eld, km/km2) and cave porosity (a fraction of the volume of a cave block, occupied by mapped cavities) are roughly one order of magnitude greater in confi ned settings than in unconfi ned. Average areal coverage (a fraction of the area of the cave fi eld occupied by passages in a plan view) is about 5 times greater in confi ned settings. Conduit permeability in unconfi ned settings tends to be highly heterogeneous, whereas it is more homogeneous in confi ned settings. The storage characteristics of confi ned karstifi ed aquifers are much greater. Recognition of the differences between origin, organisation and behaviour of karst systems evolved in unconfi ned and confi ned settings can improve effi ciency of exploration and management of various resources in karst regions and adequacy of assessment of karst-related hazards.